1. Field of the Invention
The present invention relates to a multicomponent cross-piece used in the manufacture of heddle frames for weaving looms and in particular low-noise and low-cost heddle frames for high-speed looms.
2. Description of the Related Art
As is well-known to persons skilled in the art, heddle frames are devices used in weaving looms in order to obtainxe2x80x94by means of their alternating movement actuated by the weave machine in a vertical or horizontal plane perpendicular to the weaving planexe2x80x94the movement of groups of warp yarns in accordance with a predefined weaving pattern. The movement of the heddle frames is synchronized with the insertion of the weft yarn and has an amplitude proportional to the distance between the beating-up point of the reed and the heddle frame in question, so as to obtain an angular opening of the shed which is constant in all the frames.
A Heddle frames are formed by two side-pieces which form the guides for the alternating movement of the frame and by two cross-pieces on which thin rods made of steel or other material (i.e. the heddles) are mounted, each of said heddles supporting one or more warp yarns. In order to obtain the frame structure, the side-pieces and the cross-pieces are fixed together at right angles at the four corners of the frame in a perfectly rigid mannerxe2x80x94so as to prevent any possible deformation of the frame during operationxe2x80x94and at the same time can be easily disassembled to allow insertion or extraction of the desired number of heddles for each operation.
With the improved performance of modern weaving looms, in particular the increase in the operating speed, it is of particular importance to reduce the weight of the masses performing an alternating movement and therefore also that of the heddle frames, so as to ensure that the heddle frames are able to withstand the fatigue resulting from the characteristic alternating and pulsating movement during operation thereof.
According to the prior art, therefore, various solutions have been proposed in an attempt to achieve a better compromise between the characteristics of lightness and resistance to mechanical stresses, with the use, in addition to or in place of the conventional iron-based metallic materials, of lighter materials such as aluminium, light alloys, expanded plastics, composite materials and the like, as will be briefly illustrated below with particular reference to the structure of the cross-pieces to which the present invention relates.
The cross-pieces of the known type all have a similar generic configuration, comprising a relatively thick, box-like, outer portionxe2x80x94intended to provide the frame with the necessary strength and an adequate flexural and torsional rigidity and moreover form the zone for securing of the side-piecesxe2x80x94and a thin solid inner portionxe2x80x94intended to form the heddle support elementxe2x80x94usually in the form of a lug projecting from one of the sides of the outer portion and provided at its free end with a heddle support rail often in the form of a metal section. A first conventional type of cross-piece which has a low weight, is a cross-piece the two portions of which are formed by a single extruded piece of aluminium or other light alloys. This type of cross-piece provides excellent results when it is used for the formation of heddle frames intended for low or medium speed looms, while it has too short a working life in high-speed looms, such as air looms for example. The high fatigue stresses to which the cross-piece is subject in these types of looms in fact lead to deformations or breakages of the cross-piece, in particular in the joining zone between the outer box-shaped portion and the thin, solid, inner portion of the cross-piece.
In the art, therefore, numerous other types of cross-pieces have been proposed where the cross-pieces are made with a combination of different materials which are assembled with particular processes, the object of which is precisely to ensure, for the same weight or an even lower weight, a greater structural resistance of the cross-piece. Cross-pieces provided with this new structural design may be divided into different homogeneous categories including in particular: a first category which comprises frames where the cross-piece is formed by sheets of carbon fibre which are assembled by means of gluing to a core made of expanded polyurethane or provided with a honeycomb structure (see, for example, EP-A-770,722); a second category, which comprises frames where the cross-piece is formed by a shell structure made of thin, laser-welded, sheet metal which is formed and assembled about a core made of expanded polyurethane or provided with a honeycomb structure (IT-A-MI98A002853); and, finally, a third category which comprises frames in which the cross-pieces are made using new materials known as xe2x80x9cpoltrudesxe2x80x9d which are obtained by means of a process involving the extrusion of epoxy resins or other synthetic materials on a lamellar carbon-fibre matrix.
All the latest generation frames formed using the cross-pieces from the different categories briefly described above are able to achieve a marked increase in the resistance of the frames to alternating stresses and therefore a possible parallel increase in the maximum speed of the looms with which these frames may be used without giving rise to breakages or other types of drawbacks.
Moreover, these frames, precisely because of the particular materials used and the complicated production processes, have a very high manufacturing cost, which has greatly influenced the spreading thereof in the market, and also are not entirely devoid of drawbacks. The very structural rigidity which characterises them is, in fact, the cause of a low degree of intrinsic structural damping of the vibrations such that basically this type of heddle frame has a noise level which is decidedly higher than that of conventional aluminium extruded frames. It is pointed out, in this connection, that the noisiness of the heddle frames is essentially due to the fact that the heddles are inserted into the rails of the cross-pieces with a fairly large amount of playxe2x80x94in order to assist the weaving loom operator who frequently has to move the entire heddle assembly or part of it for maintenance operations or variations in the articlexe2x80x94and this results in a continuous series of knocking of the heddles against either one of the two opposite rails to which they are fastened, said knocking which occurs during the alternating movement of the frame resulting precisely in the noisiness of the said frame.
The object of the present invention is therefore to provide a new type of cross-piece for the formation of heddle frames which allows the use of the said frames in high-speed looms, without creating problems of high cost and noisiness which are characteristic of the latest generation of frames illustrated above.
This object is achieved, according to the present invention, by means of a cross-piece for heddle frames of weaving looms, of the type comprising a thick outer portion having a box-shaped structure and a thin, solid, inner portion to which a heddle support rail is fixed, characterized in that said outer portion and said inner portion are formed by separate and distinct sections which are fixed together in position by one or more elements which are made of material which is soft or has a high mechanical hysteresis and which are arranged between said sections.
According to a characteristic feature of the invention, said seoarate and distinct sections may be made of metallic materials or composite materials, for example of the various types described above, provided that they have an adequate rigidity for withstanding the load imparted by the warp yarns via the heddles, without undergoing major deformation.
According to a characteristic feature of the invention, said outer portion comprises a cavity for housing a connecting end of said inner portion.
According to another characteristic feature of the invention, said elements made of material which is soft or has a high mechanical hysteresis consist of two profiled strips of plastic material with suitable mechanical characteristics, arranged on either side of the connecting end of said inner portion to the outer portion of the cross-piece, so as to prevent any direct contact between said portions.
According to a further characteristic feature of the invention, said profiled strips of plastic material comprise a profiled strip made of resilient material and partially covering the connecting end of the inner portion and a profiled strip made of rigid material and force-fitted between said inner portion and said outer portion, compressing said profiled strip made of resilient material and snap-engaging with a rib of the outer portion.